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On page 1 showing 1 ~ 18 papers out of 18 papers

Interactions among toxins that inhibit N-type and P-type calcium channels.

  • Stefan I McDonough‎ et al.
  • The Journal of general physiology‎
  • 2002‎

A number of peptide toxins from venoms of spiders and cone snails are high affinity ligands for voltage-gated calcium channels and are useful tools for studying calcium channel function and structure. Using whole-cell recordings from rat sympathetic ganglion and cerebellar Purkinje neurons, we studied toxins that target neuronal N-type (Ca(V)2.2) and P-type (Ca(V)2.1) calcium channels. We asked whether different toxins targeting the same channels bind to the same or different sites on the channel. Five toxins (omega-conotoxin-GVIA, omega-conotoxin MVIIC, omega-agatoxin-IIIA, omega-grammotoxin-SIA, and omega-agatoxin-IVA) were applied in pairwise combinations to either N- or P-type channels. Differences in the characteristics of inhibition, including voltage dependence, reversal kinetics, and fractional inhibition of current, were used to detect additive or mutually occlusive effects of toxins. Results suggest at least two distinct toxin binding sites on the N-type channel and three on the P-type channel. On N-type channels, results are consistent with blockade of the channel pore by omega-CgTx-GVIA, omega-Aga-IIIA, and omega-CTx-MVIIC, whereas grammotoxin likely binds to a separate region coupled to channel gating. omega-Aga-IIIA produces partial channel block by decreasing single-channel conductance. On P-type channels, omega-CTx-MVIIC and omega-Aga-IIIA both likely bind near the mouth of the pore. omega-Aga-IVA and grammotoxin each bind to distinct regions associated with channel gating that do not overlap with the binding region of pore blockers. For both N- and P-type channels, omega-CTx-MVIIC binding produces complete channel block, but is prevented by previous partial channel block by omega-Aga-IIIA, suggesting that omega-CTx-MVIIC binds closer to the external mouth of the pore than does omega-Aga-IIIA.


Either N- or P-type calcium channels mediate GABA release at distinct hippocampal inhibitory synapses.

  • J C Poncer‎ et al.
  • Neuron‎
  • 1997‎

Transmitter release at most central synapses depends on multiple types of calcium channels. Identification of the channels mediating GABA release in hippocampus is complicated by the heterogeneity of interneurons. Unitary IPSPs were recorded from pairs of inhibitory and pyramidal cells in hippocampal slice cultures. The N-type channel antagonist omega-conotoxin MVIIA abolished IPSPs generated by interneurons in st. radiatum, whereas the P/Q-type antagonist omega-agatoxin IVA had no effect. In contrast, omega-agatoxin IVA abolished IPSPs generated by st. lucidum and st. oriens interneurons, but omega-conotoxin MVIIA had no effect. After unitary IPSPs were blocked by toxin, transmission could not be restored by increasing presynaptic calcium entry. The axons of the two types of interneurons terminated within distinct strata of area CA3. Thus, GABA release onto pyramidal cells, unlike glutamate release, is mediated entirely by either N- or P-type calcium channels, depending on the presynaptic cell and the postsynaptic location of the synapse.


L-Type calcium channels mediate calcium oscillations in early postnatal Purkinje neurons.

  • P Liljelund‎ et al.
  • The Journal of neuroscience : the official journal of the Society for Neuroscience‎
  • 2000‎

Ca(2+) signaling is important in many fundamental neuronal processes including neurotransmission, synaptic plasticity, neuronal development, and gene expression. In cerebellar Purkinje neurons, Ca(2+) signaling has been studied primarily in the dendritic region where increases in local Ca(2+) have been shown to occur with both synaptic events and spontaneous electrical activity involving P-type voltage-gated Ca(2+) channels (VGCCs), the predominant VGCC expressed by Purkinje neurons. Here we show that Ca(2+) signaling is also a prominent feature of immature Purkinje neurons at developmental stages that precede expression of dendritic structure and involves L-type rather than P-type VGCCs. Immature Purkinje neurons acutely dissociated from postnatal day 4-7 rat pups exhibit spontaneous cytoplasmic Ca(2+) oscillations. The Ca(2+) oscillations require entry of extracellular Ca(2+), are blocked by tetrodotoxin, are communicated to the nucleus, and correlate closely with patterns of endogenously generated spontaneous and evoked electrical activity recorded in the neurons. Immunocytochemistry showed that L-, N-, and P/Q-types of VGCCs are present on the somata of the Purkinje neurons at this age. However, only the L-type VGCC antagonist nimodipine effectively antagonized the Ca(2+) oscillations; inhibitors of P/Q and N-type VGCCs were relatively ineffective. Release of Ca(2+) from intracellular Ca(2+) stores significantly amplified the Ca(2+) signals of external origin. These results show that a somatic signaling pathway that generates intracellular Ca(2+) oscillations and involves L-type VGCCs and intracellular Ca(2+) stores plays a prominent role in the Ca(2+) dynamics of early developing Purkinje neurons and may play an important role in communicating developmental cues to the nucleus.


A Novel Calcium Uptake Transporter of Uncharacterized P-Type ATPase Family Supplies Calcium for Cell Surface Integrity in Mycobacterium smegmatis.

  • Hemant Kumar Gupta‎ et al.
  • mBio‎
  • 2017‎

Ca2+ plays an important role in the physiology of bacteria. Intracellular Ca2+ concentrations are tightly maintained in the nanomolar range. Molecular mechanisms of Ca2+ uptake in bacteria remain elusive. Here we show that CtpE is responsible for Ca2+ uptake in Mycobacterium smegmatis It represents a previously uncharacterized P-type ATPase family in bacteria. Disruption of ctpE in M. smegmatis resulted in a mutant with impaired growth under Ca2+-deficient conditions. The growth defect of the mutant could be rescued by Ca2+ or by ectopic expression of ctpE from M. smegmatis or the orthologous gene (Rv0908) from Mycobacterium tuberculosis H37Rv. Radioactive transport assays revealed that CtpE is a Ca2+-specific transporter. Ca2+ deficiency increased expression of ctpE, resulting in increased 45Ca2+ accumulation in cells. ctpE is a gene that is part of an operon, which is negatively regulated by Ca2+ The ctpE mutant also showed hypersensitivity to polymyxin B, increased biofilm formation, and higher cell aggregation, indicating cell envelope defects. Our work establishes, for the first time, the presence of Ca2+ uptake pumps of the energy-dependent P-type ATPase superfamily in bacteria and also implicates that intracellular Ca2+ is essential for growth and cell envelope integrity in M. smegmatisIMPORTANCE Ca2+ is essential for gene regulation, enzymatic activity, and maintenance of structural integrity of cell walls in bacteria. Bacteria maintain intracellular calcium concentrations in a narrow range, creating a gradient with low cytoplasmic calcium concentration and high extracellular calcium concentration. Due to this steep gradient, active pumps belonging to family 2 of P-type ATPases and antiporters are used for Ca2+ efflux, whereas Ca2+ uptake is usually carried out by channels. Molecular mechanisms of Ca2+ uptake in bacteria are still elusive and are mainly limited to a nonproteinaceous channel in Escherichia coli and a pH-dependent channel protein from Bacillus subtilis Energy-dependent active transporters are not reported for Ca2+ uptake from any organism. Here we show that CtpE belonging to a family of previously uncharacterized bacterial P-type ATPases is involved in specific uptake of Ca2+ into Mycobacterium smegmatis We also demonstrate that intracellular Ca2+ obtained through CtpE is essential for growth and maintenance of cell surface properties under Ca2+-deficient conditions.


Frequency-dependent depression of exocytosis and the role of voltage-gated calcium channels.

  • Jaya Pamidimukkala‎ et al.
  • Brain research‎
  • 2006‎

Synaptic vesicle exocytosis in primary cultures of baroreceptor neurons is reduced during high-frequency stimulation. Calcium influx through voltage-gated calcium channels (VGCC) is a key step in neurotransmitter release. With the help of FM2-10, a marker of synaptic vesicle recycling, the present study investigates the differential contribution of several VGCC subtypes to exocytosis in neuronal processes and how this contribution is altered at high frequencies. In control experiments, field stimulation at 0.5 Hz evoked about 66 +/- 5% destaining. Combined blockade of N- and P/Q-subtypes with Ctx-MVIIC was far more effective in reducing exocytosis (11 +/- 8%) than blocking N-type (49 +/- 5%, Ctx-GVIA) or P-type (46 +/- 1%, Agatoxin) alone. The effectiveness of the blockers also varied with the duration of stimulation: Ctx-GVIA attenuating exocytosis significantly in the first 60 s and Agatoxin affecting exocytosis only towards the end of 180 s stimulation period. Field stimulation at 10 Hz evoked exocytosis (36 +/- 18%) comparable to that evoked by 0.5 Hz in the presence of Ctx-GVIA. While blockade with Agatoxin had no effects, Ctx-GVIA, Ctx-MVIIC and L-type blocker Nifedepine had small but similar inhibitory effects on exocytosis at 10 Hz. The data suggest that N-type is the major contributor to exocytosis at 0.5 Hz, and this contribution is reduced during prolonged stimulation periods and at high frequencies.


Altered functional expression of Purkinje cell calcium channels precedes motor dysfunction in tottering mice.

  • M A Erickson‎ et al.
  • Neuroscience‎
  • 2007‎

In tottering mice, a point mutation in the gene encoding P-type (Ca(v)2.1) voltage-gated calcium channels results in ataxia, absence epilepsy, and motor dystonia that appear 3-4 weeks postnatally. The aberrant motor behaviors have been linked to cerebellar dysfunction, and adult Purkinje cells (PCs) of tottering mice exhibit calcium-dependent changes in gene transcription suggestive of altered calcium homeostasis. In an attempt to identify early postnatal events important for the development of the behavioral phenotype, we examined calcium channel expression in cerebellar PCs from postnatal days 6-15 (P6-15). Whole cell recording was combined with selective calcium channel antagonists to allow discrimination of the various voltage-activated calcium channels types; early age-dependent differences between tottering and wild-type PCs were found. Wild-type PCs experienced a steady increase in P current density over this period, resulting in a twofold change by P15. In tottering, by contrast, P current density remained unchanged from P6-8 and was only 25% of the wild-type level by P8. A developmental delay in functional expression was implicated in this early deficit, since ensuing gains over the subsequent week brought tottering P current density close to the wild-type level by P15. At this age, tottering PCs also exhibited a 2.2-fold higher L-type calcium current density than that expressed by wild-type PCs. Increases in N current were apparent at some ages, most strikingly within a subset of tottering PCs at P15. Functional R- and T-type calcium current densities were equivalent to wild-type levels at all ages. We conclude that the tottering mutation brings about selective changes in functional calcium channel expression 1 to 2 weeks prior to the appearance of the behavioral deficits, raising the possibility that they represent an early, primary event along the path to motor dysfunction in tottering.


Histamine modulates high-voltage-activated calcium channels in neurons dissociated from the rat tuberomammillary nucleus.

  • Y Takeshita‎ et al.
  • Neuroscience‎
  • 1998‎

The effects of histamine on high-voltage-activated Ca2+ channels in the histaminergic neurons acutely dissociated from the rat tuberomammillary nucleus were investigated in the nystatin-perforated patch recording mode under voltage-clamp conditions. Histamine suppressed the high-voltage-activated Ca2+ channel currents in neurons which were positive for histidine decarboxylase with immunocytochemistry. The half-maximum inhibitory concentration and maximum inhibition were 2.6 x 10(-7) M and 16.6+/-1.90%, respectively. An H3 receptor agonist, R(-)-alpha-methylhistamine, mimicked the response to histamine, and thioperamide, an H3 receptor antagonist, inhibited the response to histamine. On the other hand, neither 2-methylhistamine, an H1 receptor agonist, nor dimaprit, an H2 receptor agonist, had a significant effect on the Ca2+ channel currents. Pretreatment with pertussis toxin blocked the inhibitory effect of histamine on Ca2+ channels, suggesting the involvement of Gi/Go proteins in the action of histamine. Omega-conotoxin-GVIA, omega-agatoxin-IVA, nicardipine, and omega-conotoxin-MVIIC blocked the high-voltage-activated Ca2+ channel currents by 15.6, 4.3, 27.1, and 31.2% of the total current, respectively, suggesting the existence of N-, P-, L-, and Q-type Ca2+ channels. A current that was insensitive to these blockers was also found. This residual current, "R-type", was completely suppressed by the addition of 200 microM Cd2+. Histamine significantly inhibited both the N- and P-type current components among these five types of Ca2+ channel currents. We concluded that histamine suppresses the N- and P-type Ca2+ channels in histaminergic neurons through an H3 receptor which is linked to a pertussis toxin-sensitive G-protein.


Calcium channels mediate angiotensin II-induced drinking behaviour and c-fos expression in the brain.

  • B Zhu‎ et al.
  • Brain research‎
  • 1997‎

It is widely accepted that calcium ions are critically important in both short- and/or long-lasting responses of neurons to a stimulus. We have shown previously that NMDA receptors play a role in dipsogenic responses and c-fos expression induced by intracerebroventricular (i.c.v.) infusion of angiotensin II (Ang II). Since NMDA receptors are known to be linked to receptor-operated calcium channels, this study determined whether voltage dependent calcium channels are also involved in Ang II-induced behavioural (drinking) and endocrine responses as well as c-fos expression. The antidipsogenic actions of three L-type calcium channel antagonists, nifedipine, diltiazem and verapamil on Ang II-induced drinking behaviour were studied. These bind to the dihydropyridine, phenylalkylamine and benzothiazepine sites respectively. Rats (Lister-hooded) pre-treated i.c.v. with either 25 or 100 microg nifedipine, followed by 25 pmol Ang II, drank significantly less water than controls during the first 15 min after infusion. However, rats pre-treated with i.c.v. 100 microg diltiazem or verapamil showed no change in Ang II-induced drinking behaviour. The antidipsogenic actions of N- and P-type calcium channel antagonists omega-conotoxin GVIA and omega-conotoxin MVIIC were also evaluated. Rats pre-treated with 5 pmol or 20 pmol omega-conotoxin GVIA did show a slight but not significant suppression of water intake, particularly after the higher dose. Rats pre-treated with omega-conotoxin MVIIC drank almost the same amount of water as those pre-treated with saline. Nifedipine was found to suppress both Ang II-induced corticosterone release and c-fos expression in the following areas: organum vasculosum of the lamina terminalis (OVLT), median preoptic nucleus (MNPO), hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). The results described in this paper provide evidence that calcium channels play important roles in the Ang II-induced behavioural and endocrine responses, and in the expression of the immediate-early gene c-fos. This suggests that an L-type calcium channel may participate both short- and longer-term neuronal actions of Ang II.


Beta1-integrins co-localize with Na, K-ATPase, epithelial sodium channels (ENaC) and voltage activated calcium channels (VACC) in mechanoreceptor complexes of mouse limb-bud chondrocytes.

  • M Shakibaei‎ et al.
  • Histology and histopathology‎
  • 2003‎

Interactions between chondrocytes and their extracellular matrix are partly mediated by beta1-integrin receptors. Recent studies have shown that beta1-integrins co-localize with a variety of cytoskeletal complexes, signaling proteins and growth factor receptors. Since mechanosensitive ion channels and integrins have been proposed to participate in skeletal mechanotransduction, in this study, we investigated the possible co-localization of beta1-integrins with two ion channels and a P-type ATPase in mouse limb-bud chondrocytes. The alpha subunits of Na, K-ATPase, the epithelial sodium channel (ENaC) and the voltage activated calcium channel (VACC) were immunostained in organoid cultures derived from limb-buds of 12-day-old mice using well-characterized antibodies. Indirect immunofluorescence revealed abundant expression of beta1-integrins and each of the selected systems in limb-bud chondrocytes. Two-fluorochrome immunostaining demonstrated that beta1-integrin, Na, K-ATPase, ENaC and VACC co-localize in chondrocytes. Co-imunoprecipitation experiments revealed co-localization and association of integrins with ENaC, VACC and Na, K-ATPase. Cellular responses and signaling cascades initiated by the influx of calcium or sodium through putative mechanosensitive channels may be regulated more effectively if such channels were organized around integrins with receptors, kinases and cytoskeletal complexes clustered about them. The close proximity of ATPase ion pumps such as Na, K-ATPase to chondrocyte mechanoreceptor complexes could facilitate rapid homeostatic responses to the ionic perturbations brought about by activation of mechanically gated cation channels and efficiently regulate the intracellular milieu of chondrocytes.


Activation of adenosine A1 and A2 receptors differentially affects acetylcholine release from electric organ synaptosomes by modulating calcium channels.

  • Y Satoh‎ et al.
  • Neuroscience research‎
  • 1997‎

Adenosine inhibited the release of acetylcholine (ACh) evoked by high K+ depolarization from synaptosomes isolated from the electric organ of the Japanese electric ray Narke japonica. The adenosine A1 receptor agonist N6-cyclohexyladenosine was an effective inhibitor. Conversely, in the presence of an A1 receptor antagonist, 8-cyclopentyltheophylline, adenosine potentiated the release of ACh. The A2 receptor agonist N6-[2-(3,5-dimethoxyphenyl)-2-(2-methylphenyl)ethyl] adenosine also facilitated the evoked ACh release. Thus, adenosine inhibits the evoked release of ACh via the A1 receptor while it facilitates the release via the A2 receptor. The EC50 for inhibition and facilitation by adenosine was about 1 and 41 microM, respectively. There are three known types of calcium channels (N-, P/Q- and L-type) in synaptosomes. The effects of Ca2+ channel type-specific blockers on the modulation of ACh release by adenosine A1 or A2 receptor activation revealed that inhibition by A1 receptor activation was caused via inhibition of N-type calcium channels and the facilitative effects by A2 receptor activation was mediated by potentiation of P-type calcium channels.


Observations of calcium dynamics in cortical secretory vesicles.

  • Adi Raveh‎ et al.
  • Cell calcium‎
  • 2012‎

Calcium (Ca(2+)) dynamics were evaluated in fluorescently labeled sea urchin secretory vesicles using confocal microscopy. 71% of the vesicles examined exhibited one or more transient increases in the fluorescence signal that was damped in time. The detection of transient increases in signal was dependent upon the affinity of the fluorescence indicator; the free Ca(2+) concentration in the secretory vesicles was estimated to be in the range of ∼10 to 100 μM. Non-linear stochastic analysis revealed the presence of extra variance in the Ca(2+) dependent fluorescence signal. This noise process increased linearly with the amplitude of the Ca(2+) signal. Both the magnitude and spatial properties of this noise process were dependent upon the activity of vesicle p-type (Ca(v)2.1) Ca(2+) channels. Blocking the p-type Ca(2+) channels with ω-agatoxin decreased signal variance, and altered the spatial noise pattern within the vesicle. These fluorescence signal properties are consistent with vesicle Ca(2+) dynamics and not simply due to obvious physical properties such as gross movement artifacts or pH driven changes in Ca(2+) indicator fluorescence. The results suggest that the free Ca(2+) content of cortical secretory vesicles is dynamic; this property may modulate the exocytotic fusion process.


Calcium homeostasis in Pseudomonas aeruginosa requires multiple transporters and modulates swarming motility.

  • Manita Guragain‎ et al.
  • Cell calcium‎
  • 2013‎

Pseudomonas aeruginosa is an opportunistic human pathogen causing severe acute and chronic infections. Earlier we have shown that calcium (Ca(2+)) induces P. aeruginosa biofilm formation and production of virulence factors. To enable further studies of the regulatory role of Ca(2+), we characterized Ca(2+) homeostasis in P. aeruginosa PAO1 cells. By using Ca(2+)-binding photoprotein aequorin, we determined that the concentration of free intracellular Ca(2+) ([Ca(2+)]in) is 0.14±0.05μM. In response to external Ca(2+), the [Ca(2+)]in quickly increased at least 13-fold followed by a multi-phase decline by up to 73%. Growth at elevated Ca(2+) modulated this response. Treatment with inhibitors known to affect Ca(2+) channels, monovalent cations gradient, or P-type and F-type ATPases impaired [Ca(2+)]in response, suggesting the importance of the corresponding mechanisms in Ca(2+) homeostasis. To identify Ca(2+) transporters maintaining this homeostasis, bioinformatic and LC-MS/MS-based membrane proteomic analyses were used. [Ca(2+)]in homeostasis was monitored for seven Ca(2+)-affected and eleven bioinformatically predicted transporters by using transposon insertion mutants. Disruption of P-type ATPases PA2435, PA3920, and ion exchanger PA2092 significantly impaired Ca(2+) homeostasis. The lack of PA3920 and vanadate treatment abolished Ca(2+)-induced swarming, suggesting the role of the P-type ATPase in regulating P. aeruginosa response to Ca(2+).


A Transient Receptor Potential-like Calcium Ion Channel in the Filamentous Fungus Aspergillus nidulans.

  • Hongchen Wang‎ et al.
  • Journal of fungi (Basel, Switzerland)‎
  • 2021‎

Transient Receptor Potential (TRP) proteins constitute a superfamily that encodes transmembrane ion channels with highly diverse permeation and gating properties. Filamentous fungi possess putative TRP channel-encoded genes, but their functions remain elusive. Here, we report that a putative TRP-like calcium channel, trpR, in the filamentous fungus Aspergillus nidulans, performs important roles in conidiation and in adapting to cell wall disruption reagents in a high temperature-induced defect-dependent manner, especially under a calcium-limited culture condition. The genetic and functional relationship between TrpR and the previously identified high-affinity calcium channels CchA/MidA indicates that TrpR has an opposite response to CchA/MidA when reacting to cell wall disruption reagents and in regulating calcium transients. However, a considerable addition of calcium can rescue all the defects that occur in TrpR and CchA/MidA, meaning that calcium is able to bypass the necessary requirement. Nevertheless, the colocalization at the membrane of the Golgi for TrpR and the P-type Golgi Ca2+ ATPase PmrA suggests two channels that may work as ion transporters, transferring Ca2+ from the cytosol into the Golgi apparatus and maintaining cellular calcium homeostasis. Therefore, combined with data for the trpR deletion mutant revealing abnormal cell wall structures, TrpR works as a Golgi membrane calcium ion channel that involves cell wall integration.


Altered intracellular calcium homeostasis and endoplasmic reticulum redox state in Saccharomyces cerevisiae cells lacking Grx6 glutaredoxin.

  • Judit Puigpinós‎ et al.
  • Molecular biology of the cell‎
  • 2015‎

Glutaredoxin 6 (Grx6) of Saccharomyces cerevisiae is an integral thiol oxidoreductase protein of the endoplasmic reticulum/Golgi vesicles. Its absence alters the redox equilibrium of the reticulum lumen toward a more oxidized state, thus compensating the defects in protein folding/secretion and cell growth caused by low levels of the oxidase Ero1. In addition, null mutants in GRX6 display a more intense unfolded protein response than wild-type cells upon treatment with inducers of this pathway. These observations support a role of Grx6 in regulating the glutathionylation of thiols of endoplasmic reticulum/Golgi target proteins and consequently the equilibrium between reduced and oxidized glutathione in the lumen of these compartments. A specific function influenced by Grx6 activity is the homeostasis of intracellular calcium. Grx6-deficient mutants have reduced levels of calcium in the ER lumen, whereas accumulation occurs at the cytosol from extracellular sources. This results in permanent activation of the calcineurin-dependent pathway in these cells. Some but not all the phenotypes of the mutant are coincident with those of mutants deficient in intracellular calcium transporters, such as the Golgi Pmr1 protein. The results presented in this study provide evidence for redox regulation of calcium homeostasis in yeast cells.


Inhibition of acetylcholine release from presynaptic terminals of skate electric organ by calcium channel antagonists: a detailed pharmacological study.

  • C M Richardson‎ et al.
  • Neuropharmacology‎
  • 1996‎

Release of acetylcholine (ACh) from the presynaptic terminals in skate electric organ was tested for its sensitivity to calcium channel antagonists. A pharmacological profile was established by measuring inhibition of K(+)-stimulated release of [3H]ACh from prelabelled tissue slices. Peptide antagonists of N-type (omega-conotoxins GVIA and MVIIA) and P-type (omega-agatoxin-IVA) channels had no effect, whereas both omega-conotoxins MVIIC and SVIB produced concentration-dependent inhibition and could completely block ACh release. omega-Conotoxin GVIA and omega-agatoxin IVA did not attenuate the block by omega-conotoxin MVIIC. The inorganic ions, Cd2+ and Ni2+, also produced a full inhibition of release (Cd2+ > > Ni2+) and Gd3+ a partial one. Drugs targeting L-type channels (diltiazem, nifedipine and verapamil) at low microM concentrations and a synthetic analogue of the polyamine toxin from funnel web spider venom (sFTX) at 1 mM were all non-inhibitory. Inhibition by omega-conotoxins MVIIC (IC50 25 nM) and SVIB (IC50 500 nM) was reversible and modulated by external concentrations of Ca2+. Inhibitory potency was increased by lowering and decreased by elevating external Ca2+. This "antagonistic" effect of Ca2+ was also seen with Cd2+ inhibition. The inhibitory potency of omega-conotoxin MVIIC was unaffected by predepolarisation. End plate potentials generated by release of endogenous ACh in electrically-stimulated slices were also reversibly blocked by Cd2+ and omega-conotoxins MVIIC and SVIB but were unaffected by omega-conotoxin GVIA and omega-agatoxin IVA. It is concluded that ACh release in skate electric organ depends on presynaptic calcium channels which have different pharmacological properties from established sub-types.


Contrasting Ca2+ channel subtypes at cell bodies and synaptic terminals of rat anterioventral cochlear bushy neurones.

  • J M Doughty‎ et al.
  • The Journal of physiology‎
  • 1998‎

1. Whole-cell patch clamp recordings were made from bushy cells of the anterioventral cochlear nucleus (aVCN) and their synaptic terminals (calyx of Held) in the medial nucleus of the trapezoid body (MNTB). 2. Both high voltage-activated (HVA) and low voltage-activated (LVA) calcium currents were present in acutely dissociated aVCN neurones and in identified bushy neurones from a cochlear nucleus slice. 3. The transient LVA calcium current activated rapidly on depolarization (half-activation, -59 mV) and inactivated during maintained depolarization (half-inactivation, -89 mV). This T-type current was observed in somatic recordings but was absent from presynaptic terminals. 4. On the basis of their pharmacological sensitivity, P/Q-type Ca2+ channels accounted for only 6 % of the somatic HVA, while L-, N- and R-type Ca2+ channels each accounted for around one-third of the somatic calcium current. 5. The divalent permeabilities of these native calcium channels were compared. The Ba2+/Ca2+ conductance ratios of the somatic HVA and LVA channels were 1.4 and 0.7, respectively. The conductance ratio of the presynaptic HVA current was 0.9, significantly lower that that of the somatic HVA current. 6. We conclude that LVA currents are expressed in the bushy cell body, but are not localized to the excitatory synaptic terminal. All of the HVA current subtypes are expressed in bushy cells, but there is a strong polarity to their localization; P-type contribute little to somatic currents but predominate at the synaptic terminal; L-, N- and R-types dominate at the soma, but contribute negligibly to calcium currents in the terminal.


Using Strahler's analysis to reduce up to 200-fold the run time of realistic neuron models.

  • Addolorata Marasco‎ et al.
  • Scientific reports‎
  • 2013‎

The cellular mechanisms underlying higher brain functions/dysfunctions are extremely difficult to investigate experimentally, and detailed neuron models have proven to be a very useful tool to help these kind of investigations. However, realistic neuronal networks of sizes appropriate to study brain functions present the major problem of requiring a prohibitively high computational resources. Here, building on our previous work, we present a general reduction method based on Strahler's analysis of neuron morphologies. We show that, without any fitting or tuning procedures, it is possible to map any morphologically and biophysically accurate neuron model into an equivalent reduced version. Using this method for Purkinje cells, we demonstrate how run times can be reduced up to 200-fold, while accurately taking into account the effects of arbitrarily located and activated synaptic inputs.


Functional assignment to JEV proteins using SVM.

  • Ganesh Chandra Sahoo‎ et al.
  • Bioinformation‎
  • 2008‎

Identification of different protein functions facilitates a mechanistic understanding of Japanese encephalitis virus (JEV) infection and opens novel means for drug development. Support vector machines (SVM), useful for predicting the functional class of distantly related proteins, is employed to ascribe a possible functional class to Japanese encephalitis virus protein. Our study from SVMProt and available JE virus sequences suggests that structural and nonstructural proteins of JEV genome possibly belong to diverse protein functions, are expected to occur in the life cycle of JE virus. Protein functions common to both structural and non-structural proteins are iron-binding, metal-binding, lipid-binding, copper-binding, transmembrane, outer membrane, channels/Pores - Pore-forming toxins (proteins and peptides) group of proteins. Non-structural proteins perform functions like actin binding, zinc-binding, calcium-binding, hydrolases, Carbon-Oxygen Lyases, P-type ATPase, proteins belonging to major facilitator family (MFS), secreting main terminal branch (MTB) family, phosphotransfer-driven group translocators and ATP-binding cassette (ABC) family group of proteins. Whereas structural proteins besides belonging to same structural group of proteins (capsid, structural, envelope), they also perform functions like nuclear receptor, antibiotic resistance, RNA-binding, DNA-binding, magnesium-binding, isomerase (intra-molecular), oxidoreductase and participate in type II (general) secretory pathway (IISP).


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